Advances in computer technology have enabled the further miniaturization of the components required to build computer systems. As such, new categories of computer systems have been created. One of the newer categories of computer systems is the portable, hand held, or “palmtop” computer system, also referred to as a personal digital assistant or PDA. Other examples of a portable computer system include electronic address books, electronic day planners, electronic schedulers and the like.
A palmtop computer system is a computer that is small enough to be held in the user's hand and as such is “palm-sized.” As a result, palmtops are readily carried about in the user's briefcase, purse, and in some instances, in the user's pocket. By virtue of its size, the palmtop computer, being inherently lightweight, is therefore exceptionally portable and convenient.
Flat panel reflective displays are frequently used in palmtop computer systems due to their light weight, low cost, and simplicity. Reflective displays do not emit light from an internal source but rely upon reflecting light from another source to illuminate the display. However, reflective displays have disadvantages such as being relatively thick and inefficient due to the need for a front light apparatus to illuminate the display. FIG. 1A is a sectional view of an exemplary prior art reflective display assembly in a handheld computer. In FIG. 1A, an input assembly 110 is disposed above a light guide 120 which is disposed above a reflective display 130. Light guide 120 uses microstructures 121 on its top surface to reflect light from light sources 140 down onto reflective display 130 to illuminate the display. Light guide 120 is sufficiently transparent that light reflected from reflective display 130 can pass through to allow a user to view the display.
One disadvantage associated with the reflective display assembly of FIG. 1A is the fact that light guide 120 has to be transparent in order for reflective display 130 to be visible to a user. Because of this requirement, light guide 120 is not optimized to reflect light onto reflective display 130. This leads to higher power usage to provide enough light to illuminate the display sufficiently. This in turn reduces battery life which is a critical resource for handheld computers. Furthermore, light distribution is not uniform in that the portions of the reflective display 130 closest to light sources 140 appear brighter than center portions of the display. Light diffusers, which would normally be used to distribute light more uniformly, are not normally used with reflective displays as they would degrade the display quality by interfering with the light reflected from the display surface.
Another disadvantage of reflective displays is the requirement that the input assembly (e.g., input assembly 110 of FIG. 1A) be rigid. The microstructures on the top surface of light guide 120 are fragile and damaging them could further reduce their ability to reflect light onto reflective display 130. Therefore a space 122 is maintained between the input assembly and the light guide to protect the microstructures from damage. Furthermore, the microstructures have to maintain a precise alignment relative to light sources 140 in order to channel light onto reflective display 130 as evenly as possible. Because of this requirement, input assembly 110 is usually a thick, rigid, glass assembly which prevents manufacturing a thinner, curved, or flexible display assembly.
FIG. 1B is a sectional view of a typical reflective display device such as a liquid crystal display (LCD) utilized in the prior art. A top layer 150 and a bottom layer 160 surround a liquid crystal layer 170 which has seals 180 along the edges to further contain the liquid crystal. Light is reflected from the top surface 161 of bottom layer 160 back to a viewer.
Many display technologies, such as LCDs, which rely upon a fluid layer require some sort of structure to maintain distance between the top layer (e.g., top layer 150) and a bottom layer (e.g., bottom layer 160). In FIG. 1B, glass balls 190 are used for this purpose. Glass balls 190 maintain the distance between top layer 150 and bottom layer 160 yet are small enough to be indiscernible to a user, particularly when they are in a liquid. Other structures used for this purpose include columns or pillars extending from the bottom layer to the top layer which keep the layers separate. These columns are usually glass or some sort of semi-conductor material.